As ABC sideline reporter Bonnie Bernstein ran across the Texas State Fairgrounds and a mile to her car after covering her first OU-Texas football game last year, she knew something was wrong. Her calf was cramping up, her thigh was hurting and she was having trouble breathing.

"For somebody who works out five days a week, that didn't seem quite right,” said Bernstein, 37, a former Maryland gymnast.

Berns...